The invention relates to a drive for a machine having variable-stroke reciprocating pistons; and more particularly to such a machine having a rotatably journalled shaft having an axis on which a plate is mounted so that the plate cannot rotate around the axis of the shaft during operation but. The plate can, however, be adjusted around a pin which extends transverse to the rotatably journalled shaft, so that the angle enclosed by the plate and the shaft varies. The pin is journalled in a bearing block which is adjustable in the shaft direction. Each of the pistons in the machine has a drive rod having a drive rod head. The side of the drive rod head which faces the plate has a spherical surface which cooperates with a spherical surface of a further structural member. This further structural member is itself constructed as, or cooperates with, a sliding body which bears against the contact surface of the plate.
A drive of the kind which forms the subject of the present invention is known from U.S. Pat. No. 4,077,269. In this known drive the position of the plate with respect to the shaft is varied by displacement of the bearing block in the shaft direction by means of a screw and a nut which are connected to the pin. Because the plate is guided in a guide by way of an arm and a sliding block which is pivotably connected thereto, the plate will be tilted when the pin is displaced in the shaft direction. The guiding path then determines the tilt of the plate, so that it is not only possible to vary the length of the stroke of the pistons, but also the compression ratio.
The complex shape of and the large forces occurring between the sliding block and the guide are drawbacks of this known drive.
A further drawback is that adjustment of the plate not only causes a variation of the length of the piston stroke, but also of the top dead center of the pistons. Thus, more detrimental volume is introduced.